Mitochondrial uncoupling (the uncoupling of electron transport from ATP synthesis) has recently been proposed as a novel survival mechanism for cancer cells, and reduction in free radical generation is the accepted mechanism of action. However, whether mitochondrial uncoupling occurs during the early stage of cancer development is unclear. Our initial studies have demonstrated a novel and interesting finding that during skin tumorigenesis, tumor promoters can cause mitochondrial uncoupling, leading to suppression of p53 mitochondrial translocation and subsequent apoptosis, which might serve as a novel role for mitochondrial uncoupling in tumor promotion. Extending our initial studies, we hypothesize that mitochondrial uncoupling contributes to cancer development by suppressing p53 mitochondrial translocation and subsequent apoptosis. Using in vivo and in vitro skin carcinogenesis models, we will explore our hypothesis in the following aims: Specific Aim 1: Examine whether mitochondrial uncoupling promotes mouse skin carcinogenesis. We will induce mouse skin carcinogenesis by chemical carcinogens using uncoupling protein 2 knockout (ucp2 -/-) mice. As a translational approach, we will perform skin carcinogenesis with or without topical applications of genipin, an aglycone derived from geniposide, which is found in the fruit of Gardenia jasminoides Ellisa, and also known as a specific UCP2 inhibitor. Specific Aim 2: Determine whether suppression of p53 mitochondrial translocation serves as a novel mechanism of tumor promotion by mitochondrial uncoupling. We will isolate mitochondria from the mouse skin samples, and detect the levels of mitochondrial p53 and apoptosis. We will also use ucp2 transgenic mice and transfect the ucp2 gene into the skin cell model and detect whether tumor promoter-induced mitochondrial p53 translocation and apoptosis are suppressed. Our proposal aims to explore the novel idea that mitochondrial uncoupling contributes to early carcinogenesis and suppression of p53 mitochondrial translocation serves as an important mechanism of action. If accomplished, it could bring significant contributions to our understanding of how upregulation of mitochondrial uncoupling may promote tumorigenesis; thereafter, targeting UCP2 using inhibitors (e.g. genipin) could lead to suppression of cancer development. PUBLIC HEALTH RELEVANCE: The major goal of this application is to investigate whether mitochondrial uncoupling contributes to early cancer development, and whether blocking p53 mitochondrial translocation serves as the mechanism of action. In addition, targeting uncoupling protein 2 (UCP2) as a translational approach for chemoprevention will also be studied. 1